1. Field of the Invention
The present invention relates to an automatic metering/supplying apparatus for granular substances, and more particularly to a technique that automates work for subdividing a granular silicon material used as a raw material in production of, for example, a single crystal of silicon, as well as to a technique for preventing generation of dust due to such work.
2. Description of the Related Art
Conventionally, when a single crystal of silicon is manufactured in accordance with, for example, the Czochralski method, a predetermined amount of a silicon material is first melted within a crucible disposed in a chamber, and a seed crystal is dipped into the melted silicon material. The seed crystal is then pulled upwardly so as to grow a single crystal.
In such a manufacturing process, it is necessary to prepare an initial material that is placed into the crucible at the beginning, as well as a replenishment material with which the crucible is replenished so as to compensate a decrease in the amount of the silicon material (hereinafter referred to as a "recharge material"). In order to facilitate the preparation of the initial material and the recharge material, a granular silicon material is subdivided into various amounts, and divided portions of the silicon material are packed into plastic bags, which are then sealed. During the subdividing work, a predetermined amount of a granular silicon material is scooped up, with a cup such as a polyethylene cup, from a drum that contains the granular silicon material, and is transported into a plastic bag. During such packing work, the weight of the granular silicon material in the plastic bag is measured so as to obtain a plurality of material packs that contain the granular silicon material in different amounts.
When the granular silicon material is used as a recharge material, a plastic bag holding a proper amount of granular silicon material is selected in accordance with the amount of the material to be recharged, and the granular silicon material is introduced into a replenishment tube (hereinafter referred to as a "quartz recharge tube") from the plastic bag, so that the crucible is replenished with the granular silicon material via the quartz recharge tube.
Conventionally, the work for subdividing the granular silicon material contained in the drum is manually performed by a worker. Therefore, the subdividing work is laborsome and has a problem that the accuracy of measurement varies according to differences among individuals. Moreover, there is a possibility that a foreign substance such as a heavy metal or a light element is mixed into the granular silicon material, resulting in contamination of the raw material. Also, since the granular silicon material contained in the drum cannot be directly introduced into the quartz recharge tube, the crucible, or the like, the efficiency decreases in particular when the silicon material is consumed in a large amount.
Moreover, dust produced during the handling of such a granular silicon material deteriorates the working environment.
Therefore, there has been demand for a measure that can automate the above-described subdividing work, that can prevent contamination of the raw material and eliminate variations in weight, and that can maintain high efficiency even when the raw material is consumed in a large amount. There has also been a desire to maintain the working environment clean, by taking a measure against dust.